Electrophotographic developing apparatus



March 26, 1957 c. J. YOUNG ELECTROPHOTOGRAPHIC DEVELOPING APPARATUS Filed June 30, 1953 I N V E N TOR. Liar/e0" (X 16203 JTTORNEY 61 P01. YPIISE United States Patent ELECTROPHOTOGRAPHI C DEVELOPING APPARATUS Charles J. Young, Princeton, N. J., assignor to Radio Corporation of America, a corporation of Delaware Application June so, 1953, Serial No. 365,112

10 Claims. (Cl. 118-51 The present invention relates to electrostatic printing, and, more particularly, although not necessarily exclusively, to a novel means for applying electroscopic developer material, onto a surface bearing an electrostatic image.

In accordance with the present invention, a developer mix comprising a developer powder and a ferro-magnetic carrier material is applied to a surface bearing a chargeimage in the presence of a moving magnetic field. The magnetic field is preferably continuously applied and a member, such as a paper sheet bearing a charge-image, is passed through the magnetic field. A quantity of developer mix comprising developer powder and a ferromagnetic carrier material is introduced in the field so that streamers are formed and movement is imparted to these streamers by moving the field in a novel manner whereby the streamers brush the surface bearing the charge-image and thus deposit the developer powder upon the chargeimage. In the illustrative apparatus to be described herein, the field is established between a fixed pole and a magnetic pole having a plurality of flux concentrating projections and means for causing the flux to vary as between the several projections.

An object of the present invention is to provide an improved and novel means for depositing electroscopic developer powder onto a charge-image bearing surface.

Another object of the present invention is to provide depositing means as set forth wherein the electroscopic developer powder is applied to the surface by a magnetically formed and maintained brush-like mass.

A further object of the present invention is to provide a depositing means as set forth wherein novel means are provided for agitating the brush-like mass during the depositing operation.

Yet another object of the present invention is to provide, in depositing means as set forth, magnetic means for agitating the brush-like mass.

Other objects and advantages of the present invention will, of course, become apparent and immediately suggest themselves to those skilled in the art to which the invention is directed from a reading of the following description in connection with the accompanying drawing in which,

Fig. 1 is a schematic representation of a magnetically formed brush for applying electroscopic powder to a charged surface,

Fig. 2 is similar to Fig. 1 but shows a magnetic return path for the flux,

Fig. 3 is a schematic representation of apparatus constructed in accordance with the present invention for agitating the magnetically formed brush,

Fig. 4 is similar to Fig. 3 but includes the return path for the magnetic flux,

Fig. 5 illustrates another form of apparatus embodying the present invention and includes mechanical means for agitating the brush,

Patented Mar. 26, 1957 Fig. 6 is similar to Fig. 5 but includes a poly'ph-ase electrical means for agitating the brush, and,

Fig. 7 is a fragmentary view partly in cross-section taken along the line 7-7 of Fig. 6 and looking in the direction of the appended arrows.

The apparatus to be described, embodying the invention in illustrative form, may be operated with a developer mix comprising a developer powder and a carrier material consisting of alcoholized iron, that is, iron particles free from grease and other impurities soluble in alcohol. These iron particles are preferably of relatively small size, being in their greatest dimension about .002" to .008. Generally, any of the large number of developer powders known in the art is suitable for mixing with iron particles to form a developer mix to be employed in operating the present invention. A developer powder above iron in the tribo electric series is generally suitable for developing a direct image upon a negatively charged surface or a reversed image upon a positively charged surface, and conversely a developer powder below iron in the tribo electric series is suitable for developing a reversed image upon a like negatively charged surface or a direct image upon a positively charged surface. Example of the developer powders of the first named class are powdered shellac and rosin, each pigmented with a suitable coloring material such as carbon black. An example of the second class is Vinsol resin (an extract from long leaf yellow pine stumps composed principally of an oxidized form of abietic acid and manufactured by Hercules Powder Company, 908 Market Street, Wilmington, Delaware) colored with a suitable dye such as azo oil black.

Developer mixes of the type described above for the sake of completeness of illustration and methods for employing such mixes are described and claimed in copending application of Harold G. Greig, Ser. No. 344,- 123, filed March 23, 1953, and entitled Electrostatic Printing. An example of a suitable record receiving member of the kind referred to in the following description in a form of a sheet or web is fully disclosed and claimed in a copending application of Harold G. Greig, Ser. No. 248,937, filed September 9, 1951, now abandoned, and entitled Electrostatic Printing.

Referring more in detail to the drawing, the apparatus shown in Fig. 1 is described and claimed in the aforesaid Greig application Ser. No. 344,123 in which a magnetic pole member 2 is applied to a developer mix-including the carrier particles of term-magnetic material and suitable developer powder to forma brush 4. A charge image bearing record receiving member 6 is caused to move in contact with the brush 4. As the record receiving member 6 passes in contact with brush 4, the electroscopic developer powder carried by the brush 4 is attracted to and deposited on the record receiving member 6 in accordance with the charge pattern thereon. In Fig. 2, the brush 4 is confined to a more restricted area than in the means shown in Fig. l by virtue of the fact that a magnetic return path is provided for the flux. The magnetic return path includes a backing pole piece 8 and a permanent magnet 10 coupled to the pole member 2. In the apparatus illus trated in both of these figures, the brush member 4 is stationary and the receiving member 6 is moved past the brush in the direction indicated by the adjacent arrows.

Although electrosco ic powder carried by these brushes 4 will be deposited upon the receiving member 6 as the receiving member is drawn past the stationary brushes, it has been found that a better transfer of the particles may be accomplished it means are provided to agitate the brush during the time that the receiving member is being drawn past. Thus, in Fig. 3, there is shown such means. A primary, unidirectional, field producing means is represented by pole member 12. This produces a brush 4 similar to that shown in Figs. 1 and 2. A secondary field producing means is represented by the magnetic structure 14 in which a soft iron pole piece member 16 is substantially U-shaped in cross-section and is provided with one or more exciting coils 18 which are energized by an alternating current. When thus energized, the upper tips of the U-shaped pole piece member are alternately energized to opposite magnetic polarity. Since the pole member 12 supporting the brush is unidirectionally polarized, the field between that member and the secondary magnetic means 14 will shift back and forth between the two upper extremities of the U-shaped member 16 as its polarity reverses. The shifting of the field back and forth causes a corresponding agitation of the brush 4. Such agitation is accompanied by a more efiective transfer of the electroscopic powder from the brush 4 to the receiving member 6.

In Fig. 4, a similar arrangement is shown in which a pole member 22 is used to support and maintain a brush of magnetic particles intermixed with electroscopic powder and a secondary magnetic means 24, similar to that described in the discussion of Fig. 3, is provided to agitate the brush as aforesaid. In Fig. 4, however, there is additionally shown a magnetic return path for the primary field. The return path includes a first and second soft iron bridge member 26 and 28 and a unidirectional magnetizing means such as a permanent polarizing magnet 30. The operation of the device shown in Fig. 4 is substantially similar to that shown in Fig. 3 with the distinction that the brush will be more clearly defined.

In Fig. 5, there is shown a structure wherein mechanical means are provided for agitating the brush. A unidirectional magnetic means 32 is provided to establish a brush supporting magnetic field. An upper pole member 34 supports a brush 36 in a position to be contacted by the receiving member 6. This upper pole member 34 is magnetically associated with one of the polar extremities of the unidirectional or permanent magnet 32. A lower pole member 33, which is complementary of the magnetic path, constitutes a movable member having magnetic field concentrating projections thereon. For example, as shown in Fig. 5, this lower pole member 38 may comprise a rotatable rod 40 having portions 42 of greater diameter than the main portion of the rod wrapped helically about the rod. Means such as an electric motor 44 are provided for rotating or otherwise moving the lower pole member 38. As the lower pole member 38 is rotated, the magnetic flux between the upper and lower pole member will tend to be concentrated on the higher projections 42 rather than in the valleys between the projections. Rotation of this lower pole member causes an apparent motion of the projections from one end of the pole member toward the other. This produces a wave-like agitation of the brush 36 depending from the upper or fixed pole member 34. Again, means are provided, such as a set of rollers 46, for moving the image receiving member 6 relative to the brush 36.

In Figs. 6 and 7, there is shown another form of apparatus embodying the invention which is similar to that shown in Fig. 5, with the exception that electrical rather than mechanical means are provided for causing the Wavelike agitation of the brush. Here, again, a unidirectional magnetizing means such as a permanent magnet 48 is employed to establish a primary magnetic field. An upper pole piece member 50 is magnetically associated with one of the polar extremities of the magnet 48 and maintains and supports a brush 52 in a position to be engaged by an image receiving member 6. A lower pole piece member 54 is complementary of the magnetic path of the flux established by the permanent magnet. A secondary magnetic means 56 associated with the lower pole member 54- Comprises an elongated soft iron member 58 which has a plurality of regularly spaced projections 60 extending toward the upper pole member 50. Associated with these projections 64 in energizing relation thereto is a series of energizing windings or coils 62. These coils 62 may be energized from a polyphase alternating current source 64. It may be seen that two sets of windings are provided, one for each of the two phases of input current. Each of the coils embraces two of the poles or projections 60 of the structure 58 and the windings associated with one phase overlaps the windings associated with the second phase. Such an arrangement provides a series of alternately polarized projections which shift their polarity with reversal in the polarity of the energizing current. Such shifts in polarity occur sequentially from one end of the secondary magnetic structure 56 toward the other end. This, again, creates a wave-like agitation of the brush depending from the upper pole member 50.

In Figs. 3 and 4, it will be noted that the agitation of the brush 4 occurs in the same direction as the motion of the image receiving member 6. In the apparatus shown in Figs. 5 and 6, however, the agitation of the brush is in a direction transverse to that of the direction of motion of the image receiving member.

Thus, it may be seen that there has been provided an improved means for applying electroscopic powder to an image receiving member and includes simple, effective and efiicient means for agitating a magnetically supported brush to achieve a more thorough and even distribution of the electroscopic powder carried by the brush.

What is claimed is:

1. Means for applying electroscopic powder to an electrostatically charged member through the use of a developer mix including carrier particles of magnetic material intermixed with the electroscopic powder, said means comprising, in combination, magnetic field producing means associated with the mix for forming said mix into a brush, means for moving an electrostatically charged member relative to said brush, and means for magnetically agitating said brush while said brush is in contact with an electrostatically charged member moved by said means for moving an electrostatically charged member.

2. Apparatus for developing latent electrostatic images through the use of a developer mix including carrier particles of magnetic material intermixed with electroscopic developer powder, said apparatus comprising magnetic field producing means for forming a brush of said magnetic particles, means for relatively moving, to bring into cooperative relationship, said brush and a record receiving member bearing a latent electrostatic image, and means associated with said field producing means for agitating said brush.

3. In electrostatic printing apparatus, means for developing latent electrostatic images on an image bearing member through the use of a developer mix including carrier particles of magnetic material intermixed with electroscopic developer powder, said means comprising, in combination, magnetic field producing means for forming a brush of said mix, means for moving said image bearing member in contact with said brush, and means for agitating said brush while said brush is in contact with said member.

4. In electrostatic printing apparatus, means for developing latent electrostatic images on an image bearing member through the use of a developer mix including carrier particles of magnetic material intermixed with electroscopic developer powder, said means comprising magnetic field producing means for forming a brush of said mix, means for moving said image bearing member in contact with said brush, and mechanically actuated means for agitating said brush while said brush is in contact with said member.

5. In electrostatic printing apparatus, means for developing latent electrostatic images on an image bearing member through the use of a developer mix including aromas carrier particles of magnetic material intermixed with electroscopic developer powder, said means comprising, in combination, magnetic field producing means for forming a brush of said mix, means for moving said image bearing member in contact with said brush, said magnetic field producing means including a fixed pole member and a rotatable pole member having a helical flux concentrating projection thereon, and means for rotating said rotatable pole member to vary the distribution of the flux concentration whereby to agitate said brush while said brush is in contact with said image bearing member.

6. In electrostatic printing appartus means for developing latent electrostatic images on an image bearing member through the use of a developer mix including carrier particles of magnetic material intermixed with electroscopic developer powder, said. means comprising, in combination, magnetic field producing means for forming a brush of said mix, said field producing means including a fixed pole member and a movable pole member having flux concentrating projections thereon, means for moving said image bearing member in contact with said brush, and means for moving said movable pole member to vary the distribution of the flux whereby to agitate said brush while said image bearing member is in contact with said brush.

7. In electrostatic printing apparatus, means for developing latent electrostatic images on an image hearing member through the use of a developer mix including carrier particles of magnetic material intermixed with electroscopic developer powder, said means comprising, in combination, primary magnetic field producing means for forming a brush of said mix, means for moving said image bearing member in contact with said brush, and secondary, alternating magnetic field producing means associated With said brush for agitating said brush while in contact with said member.

8. In electrostatic printing apparatus, means for developing latent electrostatic images on an image bearing member through the use of a developer mix including carrier particles of magnetic material intermixed with electroscopic developer powder, said means comprising, in combination, primary magnetic field producing means for forming a brush of said mix, means for moving said image bearing member in contact with said brush, and a secondary magnetic field producing means including a multiple pole core structure and alternating current energizing means therefor, said secondary field producing means being cooperatively associated with said primary field producing means to vary the flux established by said primary field producing means whereby to agitate said brush while said brush is in contact with said image hearing member.

9. In electrostatic printing apparatus, means for developing latent electrostatic images on an image bearing member through the use of a developer mix including carrier particles of magnetic material intermixed with electroscopic developer powder, said means comprising, in combination, primary magnetic field producing means for forming a brush of said mix, means for moving said image bearing member in contact with said brush, and secondary magnetic field producing mean including a multiple pole core structure, a first set of energizing coils associated with said core structure, a second set of energizing coils associated with said core structure and a polyphase source of energizing current, each of said two sets of coils being connected to be energized by separate phases of said polyphase source, said secondary field producing means being cooperatively associated with said primary field producing means to vary the fiux established by said primary field producing means whereby to agitate said brush while said brush is in contact with said image bearing member.

10. Electrostatic printing apparatus comprising means for supporting a member presenting a record receiving surface, a magnetic structure comprising a magnetized polar member extending laterally of said surface, a second magnetized polar member oppositely disposed with respect to said first named polar member and on the opposite side of said first named member, means to produce relative motion between said surface and said magnetized polar members, means to maintain a quantity of developer mix having magnetic properties in contact with said first named polar member whereby to provide brush like streamers of said mix, said first named polar member being located with respect to the record receiving sur-- face of said first named member so that said streamers contact said record receiving surface, and means associated with said second named polar member to provide oscillatory motion of said streamers.

References Cited in the file of this patent UNITED STATES PATENTS 573,485 Sanders et al. Dec. 22, 1896 794,647 Sutton et al. July 11, 1905 1,214,817 Osgood Feb. 6, 1917 1,218,916 Weatherby Mar. 13, 1917 1,564,731 Weatherby Dec. 8, 1925 1,729,589 Mordey Sept. 24, 1929 1,828,958 Canton Oct. 27, 1931 2,239,970 Osborne Apr. 29, 1941 2,618,551 Walkup Nov. 18, 1952 2,624,652 Carlson Ian. 6, 1953 

1. MEANS FOR APPLYING ELECTROSCOPIC POWDER TO AN ELECTROSTATICALLY CHARGED MEMBER THROUGH THE USE OF A DEVELOPER MIX INCLUDING CARRIER PARTICLES OF MAGNETIC MATERIAL INTERMIXED WITH THE ELECTROSCOPIC POWDER, SAID MEANS COMPRISING, IN COMBINATION, MAGNETIC FIELD PRODUCING MEANS ASSOCIATED WITH THE MIX FOR FORMING SAID MIX INTO A BRUSH, MEANS FOR MOVING AN ELECTROSTATICALLY CHARGED MEMBER RELATIVE TO SAID BRUSH, AND MEANS FOR MAGNETICALLY AGITATING SAID BRUSH WHILE SAID BRUSH IS IN CONTACT WITH AN ELECTROSTATICALLY CHARGED MEMBER MOVED BY SAID MEANS FOR MOVING AN ELECTROSTATICALLY CHARGED MEMBER. 